Multigrid electron tube



1947. -J. A. M CULLOUGH ,431,765

MULTIGRID ELECTRON TUBE INVENTOR JACK A. M5 CULL cue/1' HIS ATTORNEY HULTIGRID ELECTRON TUBE Filed Aug. 28, 1943 3 Sheets-Sheet 2 Z5 INVENTOR JACK 4. M9 Cu LOUGH His" ATTOEQNEZY Dec. 2; 1947.

Filed Aug. 28, 1943 3 Sheets-Sheet '5 wcc 26 F Lg.3

" ms ATTORNEY Patented Dec. 2, 1947 UNITED STATES PATENT OFFICE 2,431,765 MULTI GRH)" ELECTRON" TUBE Jack A. McCullough, Millbrae, Ca1if., assignor' to Eitel-McCullou'gh, Inc., San' Bruno, Calif., a corporation of California Application August 28, 1943, S'eriaI'No. 500,444

Claims. 1

My invention relates to a vacuum tube, and more particularly to a tetrode.

It is among the objects of my invention to provide a tube of the character described having an improved construction of and arrangement for the electrodes, and having improved means for mounting the parts within an" envelope.

The invention possesses other objects and features of advantage, some of which, with the foregoing, will be set forth in the following description of my invention. It is to be understood that I do not limit myself to this disclosure of species of my invention as I may adopt variant embodi ments thereof within the scope of the claims.

Referring to the drawings:

Figure 1 is a side elevational view of a tube embodying the improvements of my invention, with portions of the internal structure broken away.

Figure 2 is a vertical sectional View of the tube; and

Figure 3 is a fragmentary vertical sectional View showing the lower portion of the envelope with cathode and grids attached, taken in a plane at right angles to that of Figure 2.

In terms of broad inclusion, my tube comprises an envelope, a cathode and plate in the envelope, a pair of concentric grids interposed between the cathode and plate, each grid having a free end and a terminal end, cathode conductor means extending through one end of the envelope and plate conductor means extending through the other end, a pair of leads sealed to the envelope, intermediate the ends, and means supporting one of the grids on one of the leads and the other grid on the other lead. A special shield is also provided at the base of the grids, and improvements are provided in the structure of the envelope and the arrangement of the electrode mounts thereon.

In greater detail, and referring to the drawings, my preferred tube comprises a vitreous envelope having two main portions separately formed and fused together along a seal 2 lying in a plane transverse to the envelope axis. The upper portion comprises a globe-like body 3 carrying an upper neck 4. The lower envelope portion comprises a reentrant stem 6 carried by a neck section having an enlarged part I and a reduced part 8 joined at a shoulder 9. Stem 6 with its exhaust tubulation I0 is formed apart from the neck section and is fused thereto at seal H adjacent the stem flare. In assembling the tube the stem and neck sections are first united and this lower tube portion is then fused to the upper portion.

Plate 12 disposed coaxially of the envelope may be of any suitable construction. That illustrated is cylindrical in shape built up of aplurality of arcuate metallic sections welded together along longitudinal flanges which serve as heat radiating fins l3. A hemispherical cap 14 is secured to-the top of the plate as part of the mounting means and to protect the envelope against heat and electron bombardment. A plate conductor lead [6 extends through the'upper end of the envelope at seal I 'I formed at the end of neck 4, the outer end of the lead having a terminal button I8. The plate is supported on the lead by a tubular bracket 19 having fins 2|, which bracket is secured at its upper end to the lead and at its lower end to cap [4.

The cathode is preferably of the filamentary type comprising a plurality of hair-pin filaments 22 of suitable material such as thoriated tungsten. Cathode leads 23 are sealed through pinch on stem 6 and are connected by flexible extensions 24 to pins 26 mounted on a base 21 cemented to-reduced part 8 of the neck section. The lower ends of the filaments are secured to brackets 28 on leads 23' while the upper ends are caught between a pair of welded disks 29 slidable on a center rod 3|. Tension is imparted by a coil spring 32 on the center rod bearing against'a sleeve'33'. V

Coaxial grids 34 and 360i the tetr'ode are interposed between-the cathode and plate. These grids are preferably of the cage-type having upper free ends and lower terminal ends, the grid wires being secured to rings 31 and 38 at the terminal ends. A pair of downwardly and laterally extending grid leads 39 and 4| extend through the envelope neck section at seals 42 formed at shoulder 9. The grids are supported by brackets 43 and 44 secured to the terminal grid rings and to the upturned ends of the leads.

In order to protect the lower portions of the envelope against heat and electron bombardment a pan-shaped metallic shield 46 is disposed transversely of the envelope adjacent the lower ends of the electrodes. This shield is preferably secured to terminal ring 31 of the outer grid and extends outwardly toward the envelope wall above the plane where seal 2 is made. A thimblelike metallic shield 41 on the stem, secured to center rod 3| by lips 48, functions to give additional protection to the stem end which faces the opening in shield 46.

An important feature of my tube construction is that the cathode and both grids are mounted on the same portion of the envelope, namely the lower portion comprising the stem and neck sectlons shown in Figure 3. This permits the grids and cathode to be accurately aligned before the main envelope portions are finally fused together at seal 2. The preferred procedure is to seal in the cathode leads and mount the cathode structure on stem 6. Then the neck section, with grid leads 39 and 4| sealed in place, is fused to the stem at seal I I. Grids 34 and 36 are then mounted on their leads. At this time the cathode and grids are all out in the open so that these electrodes may be accurately aligned, it being understood that the cathode to grid and grid to grid spacings are quite critical. Finally, envelope portion 3 having plate I2 mounted therein is fused to the lower portion at seal 2. Since the grid to plate spacing is usually greater than that between the other electrodes, the prealigned cathode and grid assembly may be inserted into the plate and a reasonable degree of alignment obtained when seal 2 is made.

I claim:

1. An electron tube comprising an envelope, a pair of nested concentric grids in the envelope, said grids each having a free end and a terminal end, a pair of leads projecting transversely of the envelope axis and extending through the side wall of the envelope, means connected to said terminal ends supporting one of the grids on one of the leads and the other grid on the other lead, and a shield disposed adjacent the terminal ends of said grids.

2. An electron tube comprising an envelope, a pair of nested concentric grids in the envelope, said grids each having a free end and a terminal end, a pair of oppositely disposed leads projecting transversely of the envelope axis and extending through the side wall of the envelope, means connected to said terminal ends supporting one of the grids on one of the leads and the other grid on the other lead, and a shield secured to the terminal end of the outer grid.

3. An electron tube comprising an envelope, a pair of nested concentric grids in the envelope, said grids each having a free end and a terminal end, a pair of leads sealed to the envelope, a shield 45 disposed adjacent the terminal ends of said grids, and means mechanically independent of said shield and connected to said terminal grid ends supporting one of the grids on one of the leads and the other grid on the other lead.

4. An electron tube comprising an envelope, a pair of nested concentric grids in the envelope, said grids each having a free end and a terminal end, a pair of leads sealed to the envelope, a shield secured to the terminal end of the outer grid, and means mechanically independent of said shield and connected to said terminal grid ends supporting one of the grids on one of the leads and the other grid on the other lead.

5. An electron tube comprising an envelope, a transverse shield in the envelope having an aperture therein, a tubular anode in the envelope above the shield, conductor means for the anode projecting into the envelope above the shield, screen grid having a lower end registering with the shield aperture and extending upwardly Within the anode, a cathode and control grid extending upwardly within said screen grid, conductor means for the cathode projecting into the envelope below said shield, and grid supporting means projecting into the envelope, said last mentioned means including a conductor sealed to the side wall of the envelope.

JACK A. McCULLOUGI-I.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date D. 135,307 Eitel et a1. Mar. 23, 1943 1,555,677 LeBlanc Sept. 29, 1925 1,758,803 Pike May 13, 1930 1,868,443 Seibt July 19, 1932 1,886,795 Dijksterhuis Nov. 8, 1932 2,010,159 Lippincott et al Aug. 6, 1935 2,012,038 Eitel et al Aug. 20, 1935 2,017,549 Salzberg Oct. 15, 1935 2,140,832 Farnsworth Dec. 20, 1938 2,228,939 Zottu et al Jan. 14, 1941 2,236,859 Vandergrift Apr. 1, 1941 2,277,858 Skellett Mar. 31, 1942 2,352,522 Eitel et al June 27, 1944 FOREIGN PATENTS Number Country Date 170,954 Great Britain Nov. 3, 1921 329,802 Great Britain May 29, 1930 

